1. Field of the Invention
The present invention relates to inkjet recording apparatuses for recording by ejecting ink from a recording head onto a recording medium, and to methods in the inkjet recording apparatuses for estimating the amount of waste ink not used for recording. In particular, the present invention relates to a recording apparatus capable of recording by ejecting ink onto the entire surface of a recording medium, and to a method for estimating the amount of waste ink ejected outside a recording medium.
2. Description of the Related Art
Known recording apparatuses, including printers, copiers, and facsimiles, record images by forming dot patterns, based on image information, on a recording medium, such as paper or a thin plastic plate. Examples of recording methods used in such recording apparatuses include an inkjet method, a wire dot recording method, a thermal recording method, and a laser beam recording method.
These days, such recording apparatuses are required to offer high-speed printing capability, high image quality (high resolution), and less noise. Examples of recording apparatuses meeting these requirements include a recording apparatus using an inkjet method (inkjet recording apparatus). An inkjet recording apparatus allows ink (recording liquid) to be ejected from ejection outlets of a recording head, causes ink droplets to adhere to a recording medium, thereby forming images thereon. Since it is not necessary in the inkjet method to bring a recording head into contact with a recording medium, images can be recorded with a constant quality on various types of recording media.
Among inkjet recording apparatuses, a serial-type recording apparatus causing the recording head to reciprocate in a direction (main scanning direction) differing from the feed direction of a recording medium is widely known. The serial-type recording apparatus is capable of recording on recording media of various sizes even with a small recording head. With a plurality of recording heads or with a plurality of nozzle arrays on a recording head, the serial-type recording apparatus can easily accommodate multiple color recording. Moreover, with a recording method in which a recording head scans the same area of a recording medium multiple times, the serial-type recording apparatus can easily adjust the recording speed and image quality by varying the number of scans on the same area. This serial recording method has become widespread rapidly in the market because of its various advantages as described above.
Another type of recording apparatus that is known these days is capable of performing full-surface recording (also called non-blank recording), in which a recording area over which a carriage reciprocates for ejecting ink extends outside a recording medium, and thus recording on the entire surface of the recording medium can be achieved without leaving blank space on the edge of the medium.
This full-surface recording involves recording on the entire surface of a recording medium, and is also called “borderless recording” in contrast with a method of recording on a recording medium, with a border left on the edge thereof. In such a recording apparatus that can accommodate full-surface recording, a platen supporting a recording medium must be prevented from being contaminated with ink ejected outside the recording medium, that is, ink off the edge of the recording medium. Therefore, a waste ink absorber is disposed on a platen or under an opening in a platen to absorb ink ejected outside the recording medium. Such a waste ink absorber provided to achieve full-surface recording is hereinafter referred to as “platen absorber”.
However, there is a limit to the amount of ink that can be absorbed in the platen absorber. A problem thus arises in that an increase in the number of sheets for full-surface recording causes ink to overflow from a platen absorber and causes the platen to be contaminated.
For such a recording apparatus capable of performing full-surface recording, some control methods have been proposed to prevent ink from overflowing from a platen absorber.
For example, Japanese Patent Laid-Open No. 2001-301201 (corresponding to U.S. Pat. No. 6,709,088) discloses a structure where a guide unit for a recording medium is provided with an ink receiving hole in which an ink absorber is placed. This document proposes a recording apparatus having amount-of-waste-liquid summing means for summing to calculate the amount of ink ejected to an ink absorber. This document also proposes amount-of-waste-liquid summing means for summing predetermined values instead of the amount of ejected ink.
This document further proposes amount-of-waste-ink measuring means for dividing the size of a recording medium into segments in the direction of movement of a carriage (in the main scanning direction), determining the size of a dot count window, performing a dot count on each dot count window on a print buffer provided in a control circuit of the inkjet recording apparatus, thereby measuring the amount of ink in a borderless area.
To calculate the total amount of ink ejected to the ink absorber, the above-described known techniques require accurate measurement of the width of a recording medium and the size of overflow areas on the left and right sides of the recording medium, and calculation every time a recording operation is performed. Therefore, these known techniques require complex and expensive sensors and mechanisms for accurate detection and measurement of the width of a recording medium and the size of overflow areas. However, if a method for summing predetermined values is used instead to reduce the costs involved in producing the recording apparatus, accuracy in estimating the amount of waste liquid is degraded.
In another method proposed to avoid such problems, the amount of ink ejected to the ink absorber is not calculated by summing, but is estimated based on recording data (that is, data to be used for recording) stored in the print buffer. However, the method for estimating the amount of ink based on recording data in the print buffer has a problem in that sufficient accuracy cannot be maintained in some cases, depending on the size of the recording medium.
This problem will be described in detail.
The above-described Japanese Patent Laid-Open No. 2001-301201 discloses a structure in which control means creates bitmap data based on recording data transmitted from the host computer, and causes head drive means to generate driving signals based on the bitmap data. This document also discloses an apparatus supplying driving signals to a recording head on a carriage, allowing ink to be ejected through the recording head, thereby recording images on a recording medium.
During image recording, print control means sends control signals to amount-of-waste-liquid counting means. Thus, during full-surface recording, the number of ink droplets ejected to the waste ink absorber on the platen is counted. Such a structure for counting the number of ejected ink droplets requires an extremely complex and expensive control device, as the total number of ejected ink droplets must be counted at every ejection.
The above-described Japanese Patent Laid-Open No. 2001-301201 also proposes a recording apparatus for adding a predetermined value, instead of performing complex control, every scan of a carriage or every time recording is performed on a recording medium. Since the sum of predetermined values is calculated, this recording apparatus does not require a complex control mechanism, as there is no need to count the number of ejected ink droplets. However, since the same value regardless of the image to be recorded is added, the accuracy in the calculation of the amount of waste ink is low. This particularly poses a problem when the platen absorber is independently structured and cannot allow ink to be discharged therefrom.
For example, if a predetermined value to be added is set to be large, it is determined that the maximum amount of ink that can be absorbed in the absorber has been reached at a stage earlier than the number of recording media on which full-surface recording can actually be performed is reached. In this case, even if the absorber is actually capable of absorbing more ink, the recording operation is restricted so that full-surface recording can no longer be performed. On the other hand, if a predetermined value to be added is set to be small, and if images causing a large number of ink droplets to be ejected to the absorber are continuously recorded, ink may overflow from an absorber before a set value is reached. In this case, the amount of ink actually discharged is larger than the sum of the predetermined values. A problem thus arises in that the platen and the reverse side of the recording medium are contaminated with ink.
A method for estimating the amount of ink based on recording data stored in the print buffer is provided to solve the problems described above. However, accuracy in dot count for estimating the amount of ink ejected off the recording medium is significantly degraded, depending on the size of recording. The degradation in accuracy will be described in detailed in an embodiment below.